Actually, given that they’ve been extinct for quite some time now, 2007 wasn’t really a particularly good year for either terror birds, aka phorusrhacids, or for mega-ducks (on which read on), but it was a pretty good year in terms of the new material that was published on them. Phorusrhacids were covered a few times back on Tet Zoo ver 1 in 2006 (go here and here): we looked at their phylogeny, taxonomy, anatomy and palaeobiology, and at the then-new discovery of BAR 3877-11, a gigantic Patagonian skull, 716 mm long, and most similar to the skull of Devincenzia pozzi (Chiappe & Bertelli 2006). What has happened since then? Well, quite a lot…
Among phorusrhacid taxa, we looked previously at Alvarenga & Höfling’s (2003) division of the group into Psilopterinae (small and gracile; Palaeocene to Pliocene), Mesembriornithinae (mid-sized, shallow-skulled, gracile-legged; Miocene to Pliocene), Patagornithinae (mid-sized; Oligocene to Pliocene), Brontornithinae (gigantic, robust; Oligocene to Miocene), and Phorusrhacinae (mostly large, gracile-legged; Miocene to Pleistocene). Most of the groups are hardly ever written about in the literature and getting information on them has long been tricky. This was always a permanent frustration of mine, especially when some of them – in particular the brontornithines – are so amazing. Brontornithines, best known for Brontornis burmeisteri from the Miocene of Argentina, possessed incredibly stocky legs and have been imagined as avian hyaenas, bone-crunching scavengers that didn’t really run fast but were specialised for walking. There’s more discussion of them in the ver 1 post here.

Anyway, the big news is that something very strange happened to Brontornis in 2007: it was, shock horror, argued not to be a phorusrhacid at all. While it’s often been noted that Brontornis – the most robustly built and probably heaviest of phorusrhacids – would have superficially recalled gastornithids and dromornithids, recent proposals that these two groups are not gruiforms or palaeognaths as long supposed but are in fact (apparently) anseriforms led Agnolin (2007) to look anew at the detailed morphology of Brontornis. It turns out that Brontornis differs from all phorusrhacids in several respects: its hypotarsus is different in shape from that of all other phorusrhacids, its pedal phalanges (foot claw bones) are sub-triangular in cross-section (rather than sub-circular), and (based on the shape of its lower jaw) its rostrum appears to have relatively short and wide (rather than long and narrow). But… so what, maybe it was just some super-graviportal, broad-billed phorusrhacid that modified a few of the characters otherwise considered typical for the group?

Alas, there’s more, for not only does Brontornis differ from phorusrhacids in these ‘key’ features, it also shares a list of derived characters with….. anseriforms. Waterfowl. In Brontornis‘s quadrate, there are two distinct ventral condyles, the medial condyle is strongly expanded mediolaterally, the orbital process is very deep dorsoventrally as it emerges from the quadrate shaft, and the pterygoid process projects dorsally rather than just horizontally. In the mandible the dentary symphysis is relatively short (comprising less than a third the total length of the jaw) and the mandibular rami strongly diverge posteriorly [Brontornis mandible shown above, from Alvarenga & Höfling 2003]. In the tibiotarsus, the distal intercondylar notch is wide and shallow (rather than narrow and deep) and the medial condyle is elongated anteroposteriorly, and the intercotylar prominence on the proximal end of the tarsometatarsus is wide and tall (rather than narrow, or low). In these characters, Brontornis not only differs from phorusrhacids, it exhibits, time and time again, the derived condition present in members of Galloanserae, and specifically in Anseriformes (Agnolin 2007) [image below is a hilarious bit of old art I found on the web. Brontornis is here pitted against… against.. well, who knows what the hell that thing is. It has a hadrosaur’s head].

While I find it easy to think that the shapes of unguals and the widths of skulls are phylogenetically quite plastic, trifling little details of quadratic condyles and of the articular surfaces between limb bones seem less easy to dispel, so (ironically perhaps) they carry more weight. In saying this, of course, I’m reminded of the contention that braincase characters are less prone to selection and hence carry a stronger phylogenetic signal than other parts of the skeleton: a contention which, as we saw briefly in one of the SVPCA 2007 articles, is probably erroneous (Rauhut 2007). I think theory would have it that all characters are equally afflicted by homoplasy and reversal, but in reality we often can’t help but think that some features really do carry more weight than others.

Anyway, I think Agnolin made quite a strong case, and at the moment it seems that Brontornis really does look more like an anseriform than a phorusrhacid. It was a mega-duck. This is particularly neat because, as I mentioned earlier, both gastornithids (the group that includes Gastornis, the probable senior synonym (Buffetaut 1997) of Diatryma) and dromornithids (the Australian mihirungs) are now regarded as anseriforms too, so we now have three distinct groups of large to gigantic, robust-limbed, deep-skulled, flightless birds at the base of Anseriformes (though note that stronger evidence demonstrating the inclusion of the mihirungs within anseriforms wouldn’t go amiss.. and note also that not all workers are happy extending Anseriformes to include these additional groups. Rather, they regard gastornithids and dromornithids as close to Anseriformes, but not necessarily within it (e.g., Livezey & Zusi 2007)). Agnolin (2007) actually found gastornithids (represented by Diatryma) to be the most basal anseriform clade, with Brontornis and a dromornithid + Anseres clade being united by the presence of a short dentary symphysis and a dorsally directed pterygoid process on the quadrate (also of interest is that, within Anseres, Agnolin found magpie-geese and screamers to be sister-taxa). Incidentally, 2007 also saw the description of the oldest gastornithid material yet reported: a large, massively stout coracoid from the Middle Palaeocene of Walbeck, Germany (Mayr 2007). One more thing: crown-group anseriforms (like the anatoid Vegavis iaai) are now known from the Upper Cretaceous (Clarke et al. 2005), so if these phylogenetic proposals are valid, gastornithids, Brontornis and dromornithids all have ghost-lineages extending back into the Cretaceous [anseriform phylogeny as recovered by Agnolin (2007) shown below].

If gastornithids, Brontornis and dromornithids really are all down at the base of Anseriformes, what does this tell us about the early evolution of the clade? It would be tremendously cool if ducks, geese and swans descended from mostly large-bodied, deep-skulled carnivores*: another reason to heap on anseriforms more accolade than they already deserve. I’ve long held the contention that these are probaby the most amazing of birds… as I’ve said before, we’re talking about a group that exhibits ‘the evolution of carpal spurs and knobs, extreme pugnacity and territoriality, nest parasitism, creching behaviour, parental carrying of young both in the water and (!) in the air, monogamous pair-bonding, underwater copulation and the (?)reinvention of the penis, major sexual variation in tracheal structure, grass-eating and 20-minute gut carrying time, niche partitioning according to intestine size, carrion feeding on Subantarctic islands, the evolution of fern-eating, island giantism, island dwarfism, crepuscularity, serrated bill margins, filter feeding with buccal lamellae, deep-diving, species where males are flightless but females flighted, coevolution of browsing forms with spiky lobelioideaens, repeated increases and decreases in body size during phylogeny, the annual transportation of TONNES of sand… and, pant pant pant, quacking’.

Plus, don’t forget that some workers now contend that another group of awesome and famous fossil birds – the pelagornithids, pseudodontorns, odontopterygiforms or bony-toothed birds – are, though not part of Anseriformes, very closely related to them (Bourdon 2005). Bourdon proposed that anseriforms and pelagornithids should be united in a new clade dubbed Odontoanserae. I still find this hard to accept to be honest… it just seems so, so… wrong [I wanted to accompany this part of the article with a good pelagornithid illustration. To my horror, I wasn’t able to find any online. Harrumph, what kind of a world are we living in?]. Anyway, moving on…

* Exactly what gastornithids and dromornithids did for a living has been controversial. We’ll avoid that issue for now but if you want to know now see Witmer & Rose (1991), Murray & Megirian (1998) and Wroe (1999a, b).

If Brontornis isn’t a phorusrhacid, what does this mean for Physornis and Paraphysornis, the other ‘brontornithines’? Well, these taxa do not exhibit the anseriform characters that Brontornis does, and do exhibit all the phorusrhacid characters that Brontornis doesn’t. So they still are phorusrhacids, it’s just that Brontornis has been removed from among them. In view of this, the phorusrhacid ‘subfamily’ Brontornithinae needs renaming, so Agnolin (2007) formally renamed it Physornithinae, with Physornis fortis Ameghino, 1895 as the type species.

The monster Kelenken

Given that my phorusrhacid articles of 2006 were mostly inspired by the initial description of the immense skull of BAR 3877-11 (Chiappe & Bertelli 2006), it’s fitting that 2007 saw the proper description and formal naming of the taxon that this specimen represents: it’s Kelenken guillermoi Bertelli et al., 2007 [skull shown here]. Named after a ‘fearsome spirit of the Tehuelche tribe … represented as [a] giant bird of prey’ (Bertelli et al., 2007, p. 410), Kelenken has a particularly long rostrum and notably deep jugal bar, and its tarsometatarsus (which, together with a partial toe bone and some indeterminate fragments, is the only other part of the skeleton currently known) also exhibits several unique characters. It appears to be a phorusrhacine: its long, narrow rostrum ends in a wickedly sharp premaxillary hook, and its slender tarsometatarsus indicates that it was moderately gracile.

The fact that the rostrum of Kelenken is far shallower than that normally reconstructed for phorusrhacines raises the question as to how accurate traditional reconstructions of these birds have been. As we’ve seen on Tet Zoo before, the oft-figured skull of Phorusrhacos longissimus is speculative as the specimen the original sketch was based on was destroyed in the field, and figures of large phorusrhacid skulls have essentially been scaled-up versions of the skulls of smaller taxa like the patagornithines. These have very deep, and proportionally short, rostra. However, did we get it wrong in assuming that the giant taxa were similarly proportioned in cranial anatomy to smaller forms like Patagornis? Bertelli et al. (2007) argued that we did, and that we need to re-imagine the giant taxa as having had rather long, low rostra.

Given that Kelenken is presently only known from that awesome skull and from a few foot bones, we can’t make confident statements about its size. Clearly – given that the skull is over 70 cm long – this was a big bird, with a standing height of over 2 m and a mass exceeding 160 kg. This makes it huge, but not as big as the biggest elephant birds and mihirungs, some of which exceeded 300 or even 400 kg, apparently.

And that’s not all – more phorusrhacids next… Oh, and let me bring your attention to Ilja Nieuwland’s recently-initiated Phorusrhacid bibliography site. Not much there yet, but once this is up and running it’ll be awesome.

Comments

in reality we often can’t help but think that some features really do carry more weight than others.

In this case this isn’t necessary, however. Brontornis simply has more anseriform features than phorusrhacid features.

Also, braincase characters are unlikely to converge with those of the same animal on which, say, jaw characters converge. Total-evidence approach.

That said, Agnolin’s cladogram is tiny. What we really need is someone plugging hundreds of fossils into the Livezey & Zusi matrix.

Bourdon proposed that anseriforms and pelagornithids should be united in a new clade dubbed Odontoanserae. I still find this hard to accept to be honest…

What I find hard to accept about this is that she found Anseriformes and Neoaves as sister-groups, with Galliformes outside. If you have any specific questions for Estelle, she’s next door…

Exactly what gastornithids and dromornithids did for a living has been controversial. We’ll avoid that issue for now but if you want to know now see Witmer & Rose (1991), Murray & Megirian (1998) and Wroe (1999a, b).

And what about the Magnificent Mihirungs book, which argues for (at least mostly) herbivory in both clades?

Admittedly I haven’t read the paper, but is it possible that the paraphyletic series of gigantic anseriforms found by Agnolin could be an analytical artefact of convergence?

I’ve actually been hoping someone might do a reconstruction of a pelagornithid in the light of the suggested position near Anseriformes – might it look something like a gigantic merganser? All the reconstructions I’ve seen look pretty much like a big gannet.

Re pelagornithids; it’s not surprising you couldn’t find an illustration, because virtually no one knows what they look like! The literature for postcrania is really poor, despite there being (I hear) good specimens around.

I had a drawing on my website based on Greg Paul’s skeletal, but it seems to have gone now.

Possibly very stupid, non-scientist question about Anseriformes if that cladogram is true: the 3 clades nearest the base are all flightless, and only the 3 most derived clades can fly. Does that mean that flightlessness is basal for Anseriformes, and therefore ducks (etc) re-evolved flight from flightless ancestors?

Anseriforms are, in general, pretty badass. For a primarily herbivorous group of animals they’re shockingly violent. (I once came across two male Anas platyrhynchos locked in a fight while on the way to do some shopping. About an hour later, on the way back, they were still there, still fighting, feathers all around them. I tried to separate them using a rolled-up newspaper, to no avail – they went straight back at each other. And as for the stuff they do in the mating season… *shudder*… let’s just say i’ve had to correct more than one radical feminist who’s argued that rape only exists in the human species…) And i can easily imagine Branta canadensis evolving into a terror-bird-alike in a post-human ecosystem…

The phorushacids in 10,000 BC were pretty damn cool, even if they were in completely the wrong time period and continent. Any opinions on how good the reconstruction was?

Great post, as usual!
The hadrosaur-headed thing in the old illustration is probably really supposed to be a hadrosaur. I’ve seen a similar picture in black and white in a late 19th entury book called “Werden und Vergehen” by Carus Sterne (pseudonym for Ernst Krause), with a phorusracoid biting into the neck of something labeled as a hadrosaur, that looked much like the animal in this picture, except that I think it was depicted with webbed forefeet.
The idea of phorusracids fighting against hadrosaurs seemed less ridiculous around 1900 than it does today, because Ameghino assigned far too early dates to the South American strata. The Deseadan (now regarded as Early Oligocene) and everything older was supposed to be Cretaceous.

Does that mean that flightlessness is basal for Anseriformes, and therefore ducks (etc) re-evolved flight from flightless ancestors?

Far more likely that all three groups became flightless independently. The number of times flight has been lost in birds suggests that flight loss is evolutionarily fairly ‘easy’ if conditions favour it, particularly in groups of birds such as many Anseriformes which do not spend the majority of their life in the air. Among living or recently extinct Anseriformes, flight was lost in Cnemiornis, Chenonetta finschi, moa-nalo, the Hawaiian nene (a Canada goose derivative), steamer ducks (the male-flightless, female-flighted example Darren alluded to in the post), Anas aucklandica, Anas nesiotis… and that’s just the ones I can think of off the top of my head. I wouldn’t be at all surprised if I’ve overlooked a few (I can’t remember if Pachyanas chathamica could fly or not).

Excellent stuff! I didn’t know anything about Brontornis’ reassignment. It seems bizarre that so many, separate lineages among the Anseriformes achieved exceptional size. It would be fascinating to see comparative growth rate studies for these giant birds.

And, Kelenken is beautiful.

For all those interested in the presumed predatory nature of the dromornithids, I recommend Murray and Vickers-Rich’s 2003 tome “Magnificent Mihirungs.” In addition to telling you EVERYTHING known about dromornithid specimens and species before 2003, the authors engage in a fascinating criticism of the dromornithids-as-predators hypothesis put forth by Wroe. Portions of that might be available in the limited preview of the book available at books.google.com

— Re: mihirung herbivory as argued for by Murray & Vickers-Rich. I forgot to cite this book because I don’t own it, and anyway, the other refs I cited (Witmer & Rose 1991, Wroe 1999a, b) do a good job of reviewing the literature on gastornithid and dromornithid ecology respectively. We still need more study, and I’m undecided on what these birds really did. Maybe the inclusion of gastornithids and dromornithids within Anseriformes supports the herbivorous interpretations of Andors and Murray & Vickers-Rich.

— Could Agnolin’s recovery of gastornithids, Brontornis and dromornithids at the base of Anseriformes be an accidental consequence of convergence? If the characters that supported this topology were just such things as ‘reduced wing’, ‘pachyostotic limb bones shafts’, ‘reduced hallux’ etc, I’d be inclined to think so. But the fact that the characters include details of quadrate anatomy and so on suggest that the data set was not misled by convergence, as such things as the orientation of the pterygoid process and depth of the orbital process (for example) don’t obviously seem linked to lifestyle. But the danger is that this simply reflects my preconceptions and, like I said, these characters could be affected by convergence as much as any. There’s no question that more data and more study is needed.

— If three ingroups at the base of Anseriformes are flightless, have the three flighted ingroups higher up the tree (screamers, magpie-geese and anatoids) re-evolved flight? Given that all the outgroups (palaeognaths, galliforms etc) exhibit flight ability – and, as Chris noted, that the evolution of flightlessness was apparently ‘easy’ for anseriforms – it looks more likely that we’re seeing three independent developments of flightlessness… if Agnolin’s topology is correct. Bring on those basal, volant gastornithids and dromornithids ðŸ™‚

— How correct were the phorusrhacids in 10,000 BC? They were so motion-blurred and frenetic that it wasn’t possible to see any details, and what little you see of head shape in the movie didn’t give any details away. Given that one of the birds in the film climbed up a tree using its bill like a parrot, my general feeling is that they weren’t too accurate. Hey, unlike the rest of the movie then. Yes I did see it, for shame.

— Carrying young in flight… yes, believe it or don’t, this is well documented and quite widespread in waterfowl. There’s a paper on it: Johnsgard & Kear (1968) (see also Livezey (1996) for a phylogenetic take on this). Johnsgard & Kear (1968) reported carrying of young in flight in comb ducks, shelducks, Egyptian geese, kelp geese and others. The carrying of eggs and young previously credited to nightjars is now regarded as erroneous. As for woodcocks, I can’t recall…

Refs – –

Johnsgard, P. A. & Kear, J. 1968. A review of the parental carrying of young by waterfowl. Living Bird 7, 89-102.

Talking of Young being carried ont the back of waterfowl, ive seen gerebs (ok different group) and mute swans doing it this year, and one particular swam demostrated that perhaps swans wouldn’t be able to fly with them on the back. This swan, with cygnets on its back, was looking for a place to rest for the night on an island with steep banks and was going back and forth looking for a way up (a (not great thanks to poor light) photo of it here http://flickr.com/photos/ukwildlife/2508290884/ ) 30secs after it decided to flap it way straight up the bank vertical, of course flinging all th cygnets off its back, who were then stranded at the base of this mini cliff!

Wow! I knew that anseriformes were capable of producing some weird variations, but this is amazing. So under the right circumstances, might a time traveler find something like these somewhere on earth?

*Tall, long-legged grazing “geese” that migrate like zebras, carrying their young on their backs

*Huge flightless grazing “swans” that circle up around the young like musk oxen when predators approach, defending them with their long wings, which have powerful clubs and/or spurs, as well as their powerful bills

*Little brush-dwelling anatids that scramble through the branches with the aid of their spurred wings and depend on camouflage to avoid predators

Speaking of flightless ducks, Anas nesiotis (Campbell Island teal) may be flightless, but they sure can get around. They were driven to extinction by the 1940’s by introduced rats, but pretty recently a relict population was found on a small islet (Dent Island)some kilometers away, and some of these birds were captured for a captive-breeding programme. In the meantime the NZ Dept. of Conservation successfully eradicated the rats from Campbell Island.

In 2004 an expedition went down to release the captive-bred birds on Campbell Island. To their surprise they found that a single male bird had already made its way there from Dent Island under its own steam – a paddle of about 20 km…

Hey, about the Anhimidae: If it’s true that their flesh is full of air sacs, and if it’s true that the main effect of air sacs in birds/dinosaurs is to decrease the weight of a large animal . . . then could anhimids be small descendants of something that was very big?

I don’t know whether the extreme pneumatisation of screamers is related to descent from large ancestors or not, but I have always wanted to know whether or not it’s true that screamers have such an extensive air sac system that if you press on their skin, they crackle.

Given that moa-nalo seem to have evolved from mallard-like ancestors into much different animals in just a few million years at most, does make me wonder wether those giant anseriforms might not be far more derived then they at first seem. After all, moa nalo were also bigheaded, big-billed, flightless and long-legged…not too much unlike a miniature dromornithid, perhaps?

I wonder if ducks and fowl are relics of the bigger ancient radiation of Galloanserae, which included all types of big and small, ground or water-living, precocious birds and was slowly outcompeted by other birds?

Given that moa-nalo seem to have evolved from mallard-like ancestors into much different animals in just a few million years at most, does make me wonder wether those giant anseriforms might not be far more derived then they at first seem.

In that context, it’s worth noting that morphological analysis moves the moa-nalo outside the Anas clade, while the ancient DNA analysis makes them sister to the Laysan teal, well within Anas.

As far as I’m aware, all the palaeoart of dromornithids before about 1997 showed them with casuariid-like stringy feathers and short, broad bills; one such example, supposed to represent the still-unnamed Riversleigh ‘Big Bird’, stands in a diorama a few metres from where I sit. I joke with visitors that we’re going to have to take it out and shoot it one of these days.
I’d definitely recommend the Murray and Rich book, it’s been very useful (to me – not everybody has loads of smashed-up dromornithid bones to work on, though) but also a great read. With nice reconstructions by Peter Trusler of Dromornis stirtoni feathered and coloured like a black swan or magpie goose.
Lots of anseriforms (like othe predominantly herbivorous vertebrates) are opportunistic predators, so I expect droms wouldn’t pass up the odd low-hanging possum. But isn’t it the case that carnivorous birds don’t use gizzard stones? There are always masses of them – chert pebbles – among the bones of our BB’s.
And speaking of magpie goose, now a single endemic relict species; the fossil record of Anseranas in Australia is only 2-4 myo, though early Paleogene anseranatids are known from Europe and North Ametrica. Keep watching JVP for something that could have been predicted (especially if you knew how busy a certain New Zealander has been with our fossil waterbirds lately).

With regards to pelagornithids: there are, in fact, good specimens known from the west coast of the United States that include feather impressions. Those are flat, but some isolated elements from the east coast are 3-dimensional. The upshot is that there is much more information out there to reconstruct them than is generally acknowledged. I have even been able to do a mechanical analysis of launch and an aerodynamic reconstruction of Pelagornis (presented in Calvert a while back). In terms of planform, they were quite close to gannets and albatrosses. That said, their overall look, especially facially, may have been quite different.

It looks like a lot of work has been done sorting out the relationships between different types of these giant birds. I’d like to see more studies done to determine the lifestyles of these creatures, since it seems likely that there were behavioral differences related to anatomy (the gastornids, for example, not having the truly raptoral hooked beak of the Phorusrhacids.) I’ll be staying tuned! P.S. I have a book with the picture of the hadrosaur reaching out of the water and grabbing the giant bird. Not merely anachronistic, but damned silly as well!

Could it be that Brontornis was not a fierce carnivore/scavenger at all but just a mellow herbivore/frugivore ? It is often depicted fighting with all kinds of other fierce animals but why couldn’t it be a specialist feeder on hard fruits and seed pots ?